Beyond counting steps

Apple is introducing a category of metrics to HealthKit that captures the complex and important elements of human movement, all via iPhone (8 and later) and Apple Watch (4 and later).

New Mobility metrics on iPhone

• Walking speed (.walkingspeed): Rate of travel over flat ground

• Step length (.walkingStepLength): Distance between feet when walking

• Double support time (.walkingDoubleSupportPercentage): Percentage of time with two feet on the ground

• Walking asymmetry (.walkingAsymmetryPercentage): Percentage of walking when left and tight step time are different

New Mobility metrics on Apple Watch

• Stair speed up (.stairAscentSpeed): Rate of vertical ascent on stairs

• Stair speed down (.stairDescentSpeed): Rate of vertical descent on stairs

• Six-minute walk (.sixMinuteWalkTestDistance): Weekly estimate of distance that could be walked in six minutes on flat ground

How to read HealthKit data

Request authorization:

/// Request authorization from the user 
self.healthStore = HKHealthStore() 

let typesToRead: Set = [ 
  HKObjectType.quantityType(forIdentifier:-walkingSpeed)!
]

self.healthStore.requestAuthorization(toShare: nil, read: typesToRead) { success, error in 
	if !success, let error = error { 
    print("Authorization failed: \(error.localizedDescription)") 
  }
}

Fetch the data of interest in the relevant time range:

// Select a time range 
let start = Calendar. current.date(byAdding: .day, value: -30, to: dateOfInjury)
let end = Calendar.current.date(byAdding: .day, value: 60, to: dateOfInjury)

let datePredicate = HKQuery.predicateForSamples(withStart: start, end: end, options: []) 

// Query walking speeds 
let walkSpeedType = HKSampleType.quantityType(forIdentifier: .walkingSpeed)!
let sortByStartDate = NSSortDescriptor(key: HKSampleSortIdentifierStartDate, ascending: true) 

let query = HKSampleQuery(
	sampleType: walkSpeedType, 
	predicate: datePredicate, 
	limit: HKObjectQueryNoLimit, 
  sortDescriptors: [sortByStartDate]) { _, samples, _ in
  visualizeWalkSpeeds(samples)
}
self.healthStore.execute(query)